(S)-Pyroglutamic Acid, (S)-Malic Acid, and (S)-Serine as Useful Starting Materials in the Synthesis of Enantiopure Hydroxyamidines

An Efficient Synthesis of Bicyclic Amidines by Intramolecular Cyclization

“…For the formation of a bicyclic amidine, the starting material should have two nitrogen‐containing functionalities that can assemble intramolecularly to form an amidine core at the ring junction. Previous reports3, 6 indicate that the intramolecular attack of a free amino group on a lactam in the presence of a strong acid ( p ‐toluenesulfonic acid or TiCl 4 )6a in refluxing xylene, and the intramolecular attack of a Boc‐protected amino group (Boc= t ‐butoxycarbonyl) to a thiolactam under acidic conditions3a,b, 6c are reliable (Scheme ). However, the former method requires harsh reaction conditions, and the latter, too many steps from readily available organic materials although the reaction conditions are mild.…”

(1R,4bS,8aR)-(1,2,3,4b,5,6,7,8,8a,9a-Decahydro-4,9a-diazafluoren-1-yl)methanol

“…Details of the preparation of (I) are given by Ostendorf et al (2000). Crystals were obtained after recrystallization from benzene.…”

Amidines in Organic Synthesis

“…Four enantiopure hydroxyamidines were prepared from (S)-pyroglutamic acid by coupling of an (S)-malic acid derived N-allyliminium ion with b-naphthol, and from an (S)-serinederived imide [80] (Figure 3.8). Unfortunately, their application to the catalytic Michael Sterically hindered chiral DBU/DBN-related molecules designed based on (þ)-camphor lactam were applied to the Michael addition of b-keto ester with methyl vinyl ketone.…”